Toner concentration sensing apparatus having plural sensors and a flow control means for each sensor

ABSTRACT

A toner concentration sensing apparatus arranged in the circulation path of developing material in an electrostatic reproduction machine and having a housing into which some of the moving developing material is diverted. The apparatus includes means in the housing or splitting the inflowing material into a plurality of paths each of which has associated therewith a toner concentration sensing device all of which cooperate with a toner replenishing means. A timing mechanism is connected to the sensing devices for periodically controlling their operation as toner concentration sensing devices.

FIPBZIZ United States Patent I I I I John Maksymiak Penlield;

Salvatore Latone, Rochester, both of, N.Y. 731,756

May 24, 1968 Sept. 14, 1971 Xerox Corporation Rochester, N.Y.

Inventors Appl. No, Filed Patented Assignee TONER CONCENTRATION SENSINGAPPARATUS HAVING PLURAL SENSORS AND A FLOW CONTROL MEANS FOR EACH SENSOR3 Claims, 9 Drawing Figs.

U.S. Cl 250/218, 96/13, 1 18/7, 118/637, 222/1, 222/57, 356/201 Int. Cl"G011 11/00, GOln 21/22, 603g 13/00 Field of Search 250/218;

[56] References Cited UNITED STATES PATENTS 2,611,876 9/1952 Hartman250/218 3,094,049 6/1963 Snelling.. 118/637 X 3,149,650 9/1964 Horst222/57 X 3,430,606 3/1969 Pease et al. 1 18/637 3,526,338 9/1970Goodrich et al. 222/1 Primary Examiner-James W. Lawrence AssistantExaminer-T. N. Grigsby AtlorneysNorman E. Schrader, James .I. Ralabateand Bernard A. Chiama ABSTRACT: A toner concentration sensing apparatusarranged in the circulation path of developing material in anelectrostatic reproduction machine and having a housing into which someof the moving developing material is diverted. The apparatus includesmeans in the housing or splitting the inflowing material into aplurality of paths each of which has associated therewith a tonerconcentration sensing device all of which cooperate with a tonerreplenishing means. A timing mechanism is connected to the sensingdevices for periodically controlling their operation as tonerconcentration sensing devices.

PATENTED SEPI 419w FIG. 5

INVENTORS HN AKSYM IA LVA RE LATO ATTORNEYS PATENTEDSEPMIHYI 3,604,939

SHEET 3 BF 3 o '88, w w 1| 1| o :l 37 A364 NESA POWER SUPPLY THRESHOLDPOWER SUPPLY DETECTOR L l g r L gusv eo- .307

(D uFaaa no LOGIC FIG. 6

DEGEES o 9o use 270 {A 0 SHUTDOWN 5+ SAMPLE} c- CLEAN SECONDS 0 L5 3.04.5

BY l l ATTORNEYS TONER CONCENTRATION SENSING APPARATUS HAVING PLURALSENSORS AND A FLOW CONTROL MEANS FOR EACH SENSOR This invention relatesto developing apparatus and particularly, to improvements in a tonerreplenishing system particularly adapted for use in automaticcopiers/reproducers that are constructed for high speed operation.

As is well known in recent years, the steadily increasing size ofvarious industries has required an enormous increase in the amount ofpaper word that must be accomplished, maintained and made available forwide interplant circulation. In the present day commercial automaticcopiers/reproduction machines, which are adapted to produce copies ofbetween and 60 8X1 l inches sheets of copy per minute, the photoreceptordevice is moved in timed unison relative to a plurality of processingstations and the usual developer system is limited as to the amount andthe toner concentration of the developing material that can be conveyedto a development zone for the machine.

The use of photoreceptor devices moving at high speeds requirerelatively fast flowing or moving developing material in order to effectgood solid area development. With large quantities of developingmaterial being consumed, there is a need for insuring at all timesoptimum mixture conditions of the developing mixture.

It is therefore the principal object of this invention to improvecopiers/reproduction machines of the type having a fast movingphotoconductor plate by maintaining the mixture relationship of tonerparticles and carrier heads at a predetermined proportion in order toassure optimum developing con ditions.

Another object of this invention is to control automatically the amountof toner particles in an electrostatic developing system.

These and other objects of this invention are obtained by means of atoner concentration sensor apparatus having devices for conveyingdeveloper material through the sensor for sampling purposes anddirecting the diverted material across two concentration sensing devicethrough which a light beam is projected for testing and density of toneraccumulated on the sensing devices. After sampling, the diverteddeveloping material is returned to the main stream of the developermaterial.

For a better understanding of the invention as well as other objects andfurther features thereof, reference is had to the I following detaileddescription of the invention to be read in conjunction with theaccompanying drawings, wherein:

FIG. I is a cross-sectional view of a developer assembly in which thepresent invention may be incorporated;

FIG. 2 is an elevation view, with parts broken away, of the tonerconcentration sensor device used in the developer assembly;

FIG. 3 is a side view of the toner sensor with parts broken away;

FIG. 4 is a ems-sectional view taken along the line 4-4 in FIG. 2.

FIG. 5 is a fragmentary view of a detail in the toner sensor;

FIG. 6 is a schematic of the control circuit for the toner sensor ofFIG. 2.

FIG. 7 is an elevational view of the timer mechanism for the tonersensor;

FIG. 8 is an end view of the timer mechanism and;

FIG. 9 is a timing chart indicating the operative sequence of the timermechanism.

For a general understanding of the illustrated copier/reproductionmachine, in which the invention may be incorporated, reference is had.As in the electrostatic system disclosed in this patent, a light imageof a document to be reproduced is projected onto the sensitized surfaceof a xerographic plate in the form of a belt 12 (see FIG. I) to form anelectrostatic latent image thereon. Thereafter, the latent image isdeveloped by a cascade developing apparatus 14 with an oppositelycharged developing material to form a xerographic powder image,corresponding to the latent image on the plate surface. The powder imageis then electrostatically transferred to a support surface such assheets of paper to which it may be fused by a fusing device whereby thepowder image is caused permanently to adhere to the support surface.

As the developing mixture is cascaded over the xerographic belt 12,toner particles are pulled away from the carrier beads and deposited onthe belt to form powder images, while the partially denuded carrierbeads and excess toner pass off the belt and into the developer housing200 by way of the pickoff bafi'le 202. As toner powder images are formedespecially for solid area development additional toner particles must besupplied to the developing mixture in proportion to the amount of tonerdeposited on the selenium belt. To supply additional toner particles tothe developing mixture, a toner dispensing system 15 is utilized toaccurately meter toner to the developing mixture within the lowerportion of the developer housing 200.

The toner dispenser l5 dispenses a uniform quantity of toner for a givenstroke length of the metering gate 304, wherein the quantity of tonerdelivered by the toner dispenser may be varied by the number of strokesof such movement per unit of time. Accurate control of the dispensingrate for the toner dispenser can be accomplished by controlling the timein which the motor M-IO is energized and the rate of reciprocation ofthe gate 304.

In order to control the dispensing of toner from the toner dispenser 15,there is shown in FIG. 2-9, the details of an automatic toner controlsystem which ultimately controls the time of energization for thedispenser motor M-IO at start up and during continuous operation of themachine.

Basic lly, the utomatic toner dispensing system comprises a tonaatfgglmounted within the developer housing 200 by any SUI a e means whichelectrically grounds the sensor, a flat funnel bin 341 which conveyssome of the developer material passing through a slot 285 in the plate220 into the sensor 340. As shown in FIG. 1, developer material enteringthe bin 34!, slides downwardly to the left along the inclined plane ofthe bin. The plate 3 42 supports an upstanding deflector plate 344 inthe path of the downwardly moving material.. A suitable conduit isarranged to conduct the flow of the developer material that does notenter the sensor 340 back into the developing apparatus 14 for continuedcirculation of the material.

The tone sensor 340 is generally square in shape having a relativelynarrow depth, and resembling a flat box-shaped housing. It is arrangedsuch that diagonal corners are aligned with the vertical in order topermit the flow of toner into the upper corner and to permit egress fromthe sensor from the diagonally placed lower corner. Within the sensorhousing, there is positioned at the upper comer of the housing, atriangular shaped baffle element 345 which has the apex of a cometthereof facing upwardly into the path of the free-falling developermaterial which flows through a conduit 346 connnected between the uppercomer of the housing and an opening 347 formed in the bin 341. Theangled element 345 serves to split the downwardly flowing developermaterial into two separate paths of approximately equal flowing widths.The developer material flowing along the left path, as viewed in FIG. 2,slides along one leg 348 of the angled element 345 and along anextension of the leg in the form of an adjustable control gate 349 untilthe development material has its flow obstructed by a guide baffle plate350 positioned relative to the path of movement of the developmentmaterial and the plane of the gate 349. The lower end of the controlgate 349 is spaced from the guide plate 350 a narrow distance to permita controlled amount of the developer material to change its direction offlow 90, or toward the lower right corner as viewed in FIG. 2. Excessdeveloper material, or that material which does not pass between theedge of the gate 349 and the plate 350, flows around the outer endthereof along the lower angled bottom walls of the sensor 340 and to anoutlet tube to be described. The developer material now slides in thisdirection along the guide plate 350 and onto a conductive glass plate351 secured thereon and across which the developer material flows. Asensing photocell P-l is secured to the sensor housing immediately belowthe plate 351 for a purpose to be described hereinafter.

Similarly, the element 345 has a second leg which is adapted to conveydevelopment material along another path of movement upon entering thesensor 340. This leg 352 is also provided with a projecting extension inthe form of a control gate 353which directs development materialdownwardly and to the right and against a second guide plate 354positioned 90 to the flow of the development material in this trunk andrelative to the gate 353. As was the case with the guide plate 350, asecond conductive glass plate 355 is insulatingly attached to the plate354 across which development material is directed as the material ispermitted to flow through the lower edge of the gate 355 and theadjacent surface of the plate 354 in a controlled quantity manner. Alamp LMP-l is mounted immediately below the plate 355 and arranged sothat when energized, some of the lights rays therefrom will betransmitted through both NESA plates and impinge upon the photocell P-l.

The development material which has passed across the plates 351 and 355and which pass as an overflow across the ends of the guide plates 350and 354 are brought together again at the lower comer of the sensorhousing 340 and into an outlet tube 356 which is in communication withthis lower 'corner. The lower end of the pipe 356 is in communicationwith portions of the developing assembly 14 in order to returndeveloping material to the system.

Each of the sensing plates 351 and 355 has a thin transparent layer of aconductive oxide, preferably formed of NESA" glass, a trademark of thePittsburgh Glass Company, which is generally a tin oxide coated glassthat is transparent to white light. Since both plates are mirror imagesof each other, details of only one of the plates will be described. Apattern 357 is formed on the plate 351 as shown in FIG. 5 and is ofL-shape being produced by scribing through the oxide layer in order toelectrically separate the pattern 357 from the remaining portion 358.Each of the conductive portions 357, 358 are connected to a circuit tobe described hereinafter.

In order to accumulate toner in an amount fairly indicative of the totalof the total amount of toner in the developing system, the patterns 357on both plates 351 and 355 have applied thereto an electrical potentialof a polarity and amount to attract and retain toner particles for somepredetermined unit of time. During this time, the light transmissionthrough the accumulated toner on both patterns 357 will be determined interms of toner concentration for the developer material. When thepredetermined unit of time has terminated and after the toneraccumulation is sensed, the polarity on the patterns 357 of the sensingplates is reversed in order to permit the patterns to repel tonerparticles thereby effecting the cleaning of the patterns by means of thedeveloper material allowed to continue flowing across the patternsbrushing toner therefrom.

As shown in FIG. 6, the conductive portions of each of the plates 35],355 are connected in parallel and to a timer mechanism generallyindicated by the reference numeral 360, shown in detail in FIGS. 7 and8. The timer mechanism 360 is in the form of a continuously rotatingbank of cams which periodically make and break switches connected to thetoner sensor circuit. The timer comprises a motor M-6 connected to agear reduction drive mechanism 362 which has its output shaft connectedto a shaft 363 rotatably mounted on a frame 364 for the timer mechanism.The shaft 363 has mounted thereon for rotation therewith a first cam 365for controlling the electrical supply to the timer drive motor M-6during shutdown of the xerographic machine, a second cam 366 whichcontrol the time during which the accumulated toner on each of theplates 351 and 355 is sampled and, a third cam 367 which controls thepolarity upon the plates 351,355. The cam 365 assures that a positivepolarity is applied to the patterns 357 whenever the sensor is "cycledout for a purpose to be described hereinafter.

The first cam 365 is formed with a control lobe 368 which is arranged toactuate an actuator 370 for a switch 371 which is connected to asuitable source of electrical power supply to the timer motor M-6. Thismotor is energized whenever a main switch in the electrical circuit forthe machine is closed and the drive for the developing system conveyorsis activated. During the shutdown of the machine when it is stillprocessing a last copy, the switch 371 will maintain the motor M-6energized for a complete sensing cycle which, as will be furtherdescribed, lasts for about 6 seconds. The developer material used inthis last cycle is furnished from the conduit 346 which serves as a sumpfor this purpose. Closing of the switch 371 assures shutdown of themotor M-6 only when the regions 357 having a positive polarity or thatpolarity opposite that of the toner particles utilized.

Before proceeding further in the description of the timer circuit abrief description of the sensing and nonsensing mode of operation forthe toner sensor will be described in relation to the timer 360 and theelectrical power thereto.

The circuit for the toner sensor and the components thereto are arrangedand programmed so that sensing of toner concentration occursperiodically and asymmetrically, that is, for a short, predeterminedtime interval, or, after a relatively long predetermined time period.For purposes of illustration of these time periods and controls, thesensor control circuit is adapted to sample or sense the tonerconcentration accumulated upon the patterns 357 for a period ofone-tenth of a second, which period occurs after the patterns are in theattract" mode for about four-tenths of a second prior to sampling.During the attract" mode which encompasses the sampling period, thepatterns 357 are of positive polarity or that polarity opposite thepolarity on the toner particles. After approximately one-tenth of asecond for the sampling" period, the electrical power for this sensingfunction will be terminated until the next cycle. The cycle of placingthe sensor in the attract" condition, sampling, and cleaning the sensoroccurs every 6 seconds when the xerographic machine is in the continuousprint mode of operation. In the illustrated example, with the attract"mode lasting approximately fivetenths of a second and the clean" cycletive and one-half seconds, the toner density sensing is asymmetrical inits cycling.

As shown in FIG. 9, there is illustrated a series of time graphs for a 6second cycle of toner concentration sampling and control. During this 6seconds, the output shaft 363 for rotating each of the cams 365, 366 and367 makes one complete revolution. As previously stated, the switch 371is actuated by the cam lobe 368 on the cam 365 and comes into serviceonly for the last 6 second sensing cycle during processing of the lastcopy of a particular production run. The circular length of the lobe 368is such as to maintain closing of the circuit to the timer motor M-6 fornearly the entire 6 second period and as shown in FIG. 9, the switch 371is actuated to a closed position until approximately 5.85 seconds hastranspired or when the cam reaches the line 372 on the curve A. Duringuse of the machine before the last copy is being processed, the switch371 is bypassed. It is, in effect, an auxiliary AC path to assureshutdown in the "attract" mode. At the end of the 6 second period theswitch 371 is again actuated to a closed condition commencing the nextcycle of sensor control.

As shown by the time curve B, just prior to reaching the line 372, thecam 367 which actuates a normally closed switch 373 to an open positionand a normally open switch 374 to a closed position causes theseswitches to be actuated such that the normally open switch 373 closes tocause the patterns 357 to be supplied with positive potential from thepower supply 375, thereby holding the patterns in the "attract" mode.This attract mode will remain until the termination of the 6 secondcycling period. This is illustrated in the timing curve B by the line376. Simultaneous with this actuation of the switch 373 is the actuationof the normally closed switch 374 which when open prevents the flow ofnegative potential to the areas 358 of each of the sensor plates 351,355. This occurrence is illustrated in time curve C by the line 377.

After the plates 351, 355 have been placed in the attract" mode forapproximately four-tenths of a second, the cam 366 actuates a switch 378which controls activation of a control circuit in a threshold detector379 for conditioning the photocell P-l to vary its resistance inaccordance with the intensity of the light rays from the continuallyenergized lamp LMP-l. This sample" period remains for approximatelyonetenth of a second, starting from the sampling "ON" time when thephotocell P-l is energized, illustrated by the line 380 in time curve D.As shown in FIG. 8, the control end of the lobe 368 for the cam 365 isspaced angularly from the control end of the lobe 381 for the cam 366and also spaced from the control end of the lobe 382 for the cam 367,The angular relationship between the lobes 382 and 381 is such as topermit the elapsed time between the beginning of the attract" mode andthe instant that the photocell P-l is energized. The angular distancebetween the lobes 382 and 368 is such that the patterns 357 areenergized to a positive potential before the motor M-6 is deenergized inthe processing ofa last copy.

For illustrative purposes, the polarity indicated in FIGS. 5 and 6 inrelation to the sensing plates 351, 355 are those polarities of thesupply voltage when the plates are in the attract" mode. For thisinvention then, it was assumed that the charge upon toner particles isnegative and, therefore, would be attracted to the control patterns 357for each of the sensing plates. lt is also assumed that the otherconductive areas 358 are being supplied with negative DC potential. Thiselectrical configuration is merely illustrative and has been chosen fordescriptive purposes because of the particular charge chosen for thetoner particles which, as previously stated, is negative. Thepositioning then of the actuator arms for the switches 373 and 374 issuch that toner particles will be attracted to the patterns 357 andrepelled from the patterns 358.

As previously stated, in order to exhibit high sensitivity and rapidresponse time, the electrical circuit shown in FIG. 6 is adapted toperiodic sensing action, for every six second period during which thereproduction machine is in continuous operation. During the "attractmode, the toner will accumulate upon the patterns 357 and, in an amountindicative of the amount of toner in the developer material. When thetimer 360 has effected switching of the switches 373, 374 the polarityof the patterns 357 and the portions 358 are reversed where upon thepattern 357 assumed a negative polarity and the portions 358 a positivepotential. In this manner, the control patterns 357 will repel the tonercascading, down the inclined plates 351 and 355 during this portion ofthe control cycle. When the polarity is thus reversed, the patterns 357are cleaned by the cascading developer material and thereby ispreconditioned during this clean cycle for another "attract" cycle.

In order to determine the extent of toner concentration that asaccumulated on both control patterns 357, the toner sensor 340 isprovided with the photocell lamp combination P-1 and LMP-1. Aspreviously stated, the photocell is positioned adjacent the lowersurface of the plate 351 so that toner partii cles cascading through thetoner sensor and accumulating upon both regions 357 will intercept lightrays from the lamp LMP-l positioned behind the lower surface of theother plate 355. The photocell P-l in effect will see light rays whichtraverses the cascading developer stream flowing upon both plates 351,355 and, the accumulated toner particles on each of the patterns 357.

Electrically the photocell P-l is connected to the threshold detector379 in form of a Schmitt trigger which is adapted to produce a pulsewhen the resistance in the photocell attains a predetermined valueindicative of the intensity of the light rays that reach the photocellfrom the lamp LMP-l during the "sample" cycle. The detector 379 derivesits power from a power supply 386 which also supplies the lamp LMP-lwiith its electrical energy.

The pulse generated from the Schmitt trigger 379 is fed to a machinelogic circuit 387 which, when combined with other necessary signals fromthe reproduction machine, is fed to a timer relay 388 by way of anamplifier 390 and then to the toner dispenser motor M-10 connected inseries with the relay contact for the relay 388. The timer relay 388 isarranged to remain "ON" for any adjustable predetermined time period foreach pulse thereto from the threshold detector 379. For each pulse fedto the timer relay, the motor M-lO will remain energized until the timerperiod, which may be in the range from 1-10 seconds, has terminatedwhereupon the motor M-10 will become deenergized for that pulse. Aspreviously stated during energization of the motor M-10 the meteringgate 304 is cyclically moved.

During normal operation of the automatic toner dispensing apparatus, thelight source LMP-l is continuously energized for presenting light forboth plates 351 and 355 arranged optically in series. The light rayswhich traverse both of these plates impinges upon the photocell P-lwhich is compared with predetermined values in the Schmitt trigger 379,ln the event that the predetermined value is not exceeded during thesampling step wherein the photocell is energized, the excess is utilizedto produce a pulse which is fed to the logic 387 as an indication thatthe toner concentration in the development material is below a desiredlevel.

As the density of the toner that cascades over the sensing plates 351,355 increases, the signal on the photocell P-l will be in balance withthe predetermined value in the Schmitt trigger 379 thereby terminatingperiodic energization of the motor M-l0.

lt g be apprgciated that with the presence of both sensing plates 5, thesensitivity of the sensing circuit is relatively high since there is amuch wider range of variation that light rays may experience in reachingthe photocell P-l. This also results in the control of a relatively widedensity range that the xerographic reproductions may attain, or in otherwords, the density that the toner concentration maintains can be closelyregulated. With this narrow range of variations and with continuousshort sampling time per unit of time, the xerographic machine is capableof experiencing a relatively narrow, high quality contrast control sincethe slightest unbalance will demand toner and produce replenishmentthereof.

While there is in this application specifically described one form whichthe invention may assume in practice, it will be understood that thisform of the same is shown for purposes of illustration, and that theinvention may be modified and embodied in various other forms withoutdeparting from the scope of the appended claims.

What is claimed is:

1. A toner sensing arrangement use in an electrostatic reproductionmachine of the type using developing material containing toner particlesand having a developing system which circulates the developing materialin a continuous path of movement the developing material being utilizedto produce a developed image from an electrostatic latent image andhaving a toner sensing housing, means arranged in the path of movementfor the developing material for diverting some of the material andconveying the same into the housing and means positioned in the housingfor forming a plurality of flow paths of the conveyed developingmaterial, the improvement comprising flow control means associated witheach of said paths for effecting a predetermined amount of flow of thematerial in the respective paths and thereby produce a control path foreach of said flow paths,

a plurality of devices sensitive to a condition of the toner in thedeveloping material arranged in the housing so that each of said controlpaths has one of said sensitive devices associated therewith,

7 8 and condition responsive means connected to all of said developingmaterial for formingaplurality off'low paths of the sensitive devicesfor determining the extent of a condition developing material, theimprovement comprising of the toner particles as the material comesunder the inflow control means associated with each of said paths foreffluence of all the devices. fecting a predetermined amount of flow ofthe material in 2. The toner sensing arrangement of claim 1 wherein said5 the respective paths and thereby produce a control path sensitivedevices are in the form of a transparent conductive for each of saidflow paths, m terial nd a o t ol th of h d v l i i l i h a plurality ofdevices sensitive to a condition of the toner in housing is directedacross a surface of a sensitive device. h e op ng ri l rr ng d S thal eah of Said COD- 3. A toner sensing arrangement for use in anelectrostatic PathS has one Of the Sensitive devices o i tedreproduction machine of the type using developing material containingtoner particles and having a developing system 531d fl f fesponslve aconnected to offald which circulates the developing material in acontinuous path Sensmve devlces for determmmg the extem ofa condmo" ofthe toner particles as the material comes under the inof movement thedeveloping material being utilized to fluence of all the devices.

produce a developed image from an electrostatic latent image and havingmeans arranged in the path of movement for the

1. A toner sensing arrangement use in an electrostatic reproductionmachine of the type using developing material containing toner particlesand having a developing system which circulates the developing materialin a continuous path of movement the developing material being utilizedto produce a developed image from an electrostatic latent image andhaving a toner sensing housing, means arranged in the path of movementfor the developing material for diverting some of the material andconveying the same into the housing and means positioned in the housingfor forming a plurality of flow paths of the conveyed developingmaterial, the improvement comprising flow control means associated witheach of said paths for effecting a predetermined amount of flow of thematerial in the respective paths and thereby produce a control path foreach of said flow paths, a plurality of devices sensitive to a conditionof the toner in the developing material arranged in the housing so thateach of said control paths has one of said sensitive devices associatedtherewith, and condition responsive means connected to all of saidsensitive devices for determining the extent of a condition of the tonerparticles as the material comes under the influence of all the devices.2. The toner sensing arrangement of claim 1 wherein said sensitivedevices are in the form of a transparent conductive material and acontrol path of the developing material in the housing is directedacross a surface of a sensitive device.
 3. A toner sensing arrangementfor use in an electrostatic reproduction machine of the type usingdeveloping material containing toner particles and having a developingsystem which circulates the developing material in a continuous path ofmovement the developing material being utilized to produce a developedimage from an electrostatic latent image and having means arranged inthe path of movement for the developing material for forming a pluralityof flow paths of the developing material, the improvement comprisingflow control means associated with each of said paths for effecting apredetermined amount of flow of the material in the respective paths andthereby produce a control path for each of said flow paths, a pluralityof devices sensitive to a condition of the toner in the developingmaterial arranged so that each of said control paths has one oF thesensitive devices associated therewith, said condition responsive meansconnected to all of said sensitive devices for determining the extent ofa condition of the toner particles as the material comes under theinfluence of all the devices.